Small engines of less than 50 horsepower (37.4 kilowatts) are widely used in applications such as garden tractors, lawn mowers, portable generating sets and small boat marine applications. Such engines typically employ a fuel tank mounted proximate the engine and arranged for gravity feed of fuel from the tank to the engine carburetor, although in applications approaching 50 horsepower fuel pumps may be employed in certain applications.
Heretofore, small engines have not been subject to fuel vapor emission requirements as are of motor vehicles; however, it has recently been mandated that small engines for such applications to have fuel systems which prevent vapor emission to the atmosphere both during engine operation and during periods of engine shut down. *Fuel tanks for small engines typically employ an open vent in the fuel filler cap for passage of make-up air as fuel is withdrawn during engine operation; and, to prevent pressure build up in the tank from fuel vapor.
The requirement that the tank vent be sealed has caused additional complexity and cost in reworking small engine fuel systems to meet the vapor emission requirements, particularly because engines of this type are manufactured in very high volume and the tooling is of the permanent type and represents a significant expenditure. Requirements for changes in design of the fuel system and fuel tanks will thus result in substantial increase in cost for the engine manufacture. Accordingly, it has been desired to provide a way or means of implementing fuel vapor emission controls to small engines without requiring extensive redesign and retooling of the fuel tank and fuel system components.
Thus it has been desired to minimize the amount of space required for the additional components required to provide the sealed tank system for controlling fuel vapor emission in such small engines.